Dr.rer.agr. BDR Prasantha, Dept. Food Science &Technology, Faculty of Agriculture, University of Peradeniya | 1 BENZOIC ACID C 6 H 5 COOH or C 7 H 5 NaO 2 andp-hydroxybenzoic acid (paraben) Benzoic acid Synthesis from toluene BA- naturally ester in many plant and animal Most berries contains 0.05% BApresent as part of hippuricacis (N-benzoylglycine) in mammalian urine : Humans produce 0.44 g/L BA use fungal skin diseases Na-benzoate:1 st food chemicalpreservative E numbers –E210, E212 and E213 Antimicrobial agent for large number of foods Antimicrobial activity Inactive at pH ≈ 7 More active at low pH Undissociation forms at low pH Na-benzoate effective at pH 2.5 – 4.0 Inhibit the some bacteria @ 50 - 500 ppm Inhibit yeast and mold @ 100 - 500 ppm Fruit juices > 1% (maximum) benzoates develop disagreeable taste “peppery or burning”taste Soft drinks (???) Sauces Salad dressing Margarine Pickles Use as medicine and cosmetic agent p-hydroxybenzoichighly effective on MO: 10–100 ppm, totally inhibit gram +ve and gram-ve bacteria Heptylparaben: Beer-12 ppm Fruit drink and Beverage - 20 ppm
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Dr.rer.agr. BDR Prasantha, Dept. Food Science &Technology, Faculty of Agriculture, University of Peradeniya | 1
BENZOIC ACID
C6H5COOH or C7H5NaO2
andp-hydroxybenzoic acid (paraben)
Benzoic acid Synthesis from toluene
BA- naturally ester in many plant and animal
Most berries contains 0.05%
BApresent as part of hippuricacis (N-benzoylglycine) in mammalian urine : Humans produce 0.44 g/L
BA use fungal skin diseases
Na-benzoate:1st food chemicalpreservative
E numbers –E210, E212 and E213
Antimicrobial agent for large number of foods
Antimicrobial activity
Inactive at pH ≈ 7
More active at low pH
Undissociation forms at low pH
Na-benzoate effective at pH 2.5 – 4.0
Inhibit the some bacteria @ 50 - 500 ppm
Inhibit yeast and mold @ 100 - 500 ppm
Fruit juices > 1% (maximum) benzoates develop disagreeable taste “peppery or burning”taste
Soft drinks (???)
Sauces
Salad dressing
Margarine
Pickles
Use as medicine and cosmetic agent
p-hydroxybenzoichighly effective on MO:
10–100 ppm, totally inhibit gram +ve and gram-ve bacteria
Heptylparaben:
Beer-12 ppm
Fruit drink and Beverage - 20 ppm
Dr.rer.agr. BDR Prasantha, Dept. Food Science &Technology, Faculty of Agriculture, University of Peradeniya | 2
Intracellular pH < 5 anaerobic fermentation glucose through phosphofructokinase
Benzoic acid show synergetic effect with both sorbic acid and SO2
Mode of action of chemical preservatives
Taken up by respiring MO cells
Block the oxidation of glucose and pyruvate at acetate level
Inhibit the cellular uptake of substrate
Soluble in cell membrane: act as proton ionophores
Proton leakagehigh into cells: High E needs to maintain cell pH
Disruption in cell membrane activity:low AA transport
SORBIC ACID
Ca, Na or K salt of sorbic acid (CH3CH-CHCH-CHOOH)
Slightly soluble in water and sublime
Maximum use upto 0.2%
Effective against molds andyeastsand some bacteria
More effective in acidic media pH < 6
Sorbic more effective > propionates and benzoates
Effectiveness:
Sorbic acid>Na-benzoates at pH 4 - 6
SA:used for cakes, filling for chocolates and cheese spreads at higher levels than propionates without
adding flavor
Resistance of the lactic acid bacteria at pH > 4.5:
Use as fungistat for lactic fermentation
Effective against:
Staphylococcus aureus
Salmonella
Coliforms
Pseudomonads
Vibrio parahaemolyticus
Sorbates use as fungistats:
Meat, Fish, Cheeses, Bakery product, Fruit juices, Beverages,Salad dressing
Sorbates can use with nitrites for meat product
Mode of action
Inhibition of the dehydrogenase enzyme system Lipophilic acids, sorbate, benzoate and propionate inhibit
MO cell: proton motive force (PMF)
Dr.rer.agr. BDR Prasantha, Dept. Food Science &Technology, Faculty of Agriculture, University of Peradeniya | 3
PROPIONATES
Propionic acid is a 3C acid CH3CH2COOH, act as a mold inhibitor
Short-chain FA: affect the cell membrane permeability
It has fungistatic than fungicidalaction
Little or no inhibition of most yeast and bacteria
Low inhibitory effects on yeasts:
Good for bakery dough
Ca and Na salts of propionic acid permitted:
Breads, cakes, cheese
It is found naturally in Swiss cheese
Most active in low acid foods
Propionate ≡ benzoate and sorbate
SULFUR DIOXIDE AND SULFITES
Forms: SO2, SO3
-2, SO3
-1, S2O5
-2, HSO3-1
Potassium metabisulphite (K2S2O5)
Sodium metabisulphite (Na2S2O5)
K2S2O5(s) → K2SO3(s) + SO2 (g)
SO2gas is mixed with H2O- salts of sulfurous acid is formed
Sulfurous acid
Bisulfite ion
Sulfite ion
Most foods pH 3-7
Most prevalent is bisulfite and little sulfite (IV) ions
Sulfite ion can oxidize
SO32-
+ 1/2 O2 SO4
2-
The reaction is irreversible
It consumes O2and limits the oxidation of other compounds
Free, bound and total forms of SO2
KMS/SMS is more preferable due to food pH 3-6 HSO3-
Dr.rer.agr. BDR Prasantha, Dept. Food Science &Technology, Faculty of Agriculture, University of Peradeniya | 4
SO2gas, liquid, acid salts or natural forms:
Dried fruit
Lemon juice
Molasses
Wines
Fruit juicesetc.
Sulfites (SO3
-2) react with food constituents: nucleotides, Sugars, Disulfide bonds etc.
Bisulphite ion (HSO3-1
) andSO2: inhibitbacteria than yeasts and molds
SO2 : Antimicrobial and Antioxidant activity
Bcteriostatic against Acetobacterspp. andLactic acid bacteria at low pH
Control acetic acid producing malolactic bacteria in beverages
The effectiveness is enhanced at low pH
Use for fruit and vegetable dehydration
Prevent non-enzymatic browning of process foods i.e: soup mixtures
SO2 widely used as a preservative in fruit pulps
Pork: SO2 ≥ 100 ppm inhibit the spores of C. botulinum
Sausages: 600 ppm sodium metabisullfiteinhibit the salmonellaespp.
Aerobic are more sensitive than fermentative
Yeasts forms SO2 during fruit juice fermentation
SO2 react with vitamin B1 and Anthocyanin
Antioxidant
SO2protects graph juice and wine from excessive oxidation
SO32-
+ 1/2 O2 SO4
2- (consume O2)
Anti-enzymatic
SO2inhibits oxidation enzymes and destroys them with time
Inhibits the polyphenol oxidase (PPO) oxidative reactions in juice and fresh cut fruits
Taste
SO2 will bind with acetaldehyde: "fresher" aroma in a wine
SO2 increase the extraction of flavonoid phenols(bitterness and astringency)
Fermentation
At low levels SO2 delays the fermentation, but later speeds up the multiplication of yeasts
Color
Wines fermented with SO2: retain color
Excessive amounts of SO2: discoloration of red pigments
Dr.rer.agr. BDR Prasantha, Dept. Food Science &Technology, Faculty of Agriculture, University of Peradeniya | 5
Anti-Browning
Enzymatic and Non-enzymatic browning
Enzymatic browning – discoloration of fresh cut surface of fruits and vegetables due to
polyphenol oxidase (PPO) and peroxydase (POD)
Phenol Melanins
SO2 inhibits PPO
Reduces enzymatic browning by obstructing PPO and POD
With KMS
Diphenol
Colorless Colorless
Non-enzymatic browning of process foods due to heating or storage
i. Maillardrection
ii. Caramalization
iii. Ascorbic acid oxidation
Anti-microbial
Low concentrations, SO2 inhibit the development of microorganisms.
High concentrations, destroy microbial population
Mode of action: 1. Lowering the pH of foods
2. Antimicrobial - due to strong reducing power
3. Inhibit the enzymatic browning (drying)
4. Reduction of disulfide bonds (effect on enz.)
5. Reaction with ketone
6. Inhibition of respiratory mechanism
Sulphites have been associated food intolerance symptoms
Headaches
Irritable bowel symptoms
behavior disturbance
Skin rashes
Asthma
Eye Irritation
Dr.rer.agr. BDR Prasantha, Dept. Food Science &Technology, Faculty of Agriculture, University of Peradeniya | 6
Organisms affected C. botulinum Nitrite has anti-botulinal effects
Inhibition of vegetative cell growth and spores that survive from heat or smoke
C. botulinum, C. butyricum, C. sporogenes, perfringens, S. aureus, Salmonellae spp.
Lactic acid bacteria are resistance to nitrite
Dr.rer.agr. BDR Prasantha, Dept. Food Science &Technology, Faculty of Agriculture, University of Peradeniya | 7
Nitrosamines
Nitrite + 2ry
amines => nitrosamines
Many nitrosamines are carcinogenic:
H+
R2NH2 + HONO R2N-NO + H2O
Dimethylamine reacts with nitrite to form N-nitrosodimethylamine
N-H + NO2 N-N= O
Secondary amines, tertiary amines and quaternary ammonium compounds also yields nitrosamines
Nitrosamines exist in cured meat and fish product (at low level)
Isoascorbatehas an inhibitory effect on nitrosamine formation
Therefore, nitrite-sorbate (low level) can be used for curing
Effect of Nitrite and Sorbate on production of toxin in Bacon by C. botulinum (for types A and B) at 27 oC during 60 days
Treatment Toxigenic%
Control 90
0.26% sorbate 58.8
0.26% sorbate + 40 ppm NaNO2 22
0.26% sorbate + 80 ppm NaNO2 00
120 ppm NaNO2 00.4
Mode of Action
Nitrite inhibits bacteria (ie: C. botulinum) by interfering with Fe-S enzymes/ protein thus prevent the synthesis of ATP from pyruvate and leads to an accumulation of pyruvate. In the breakdown of pyruvate:
SALT AND SUGAR
Salt (i.e. NaCl)
Slat (saline) in water at 0.8-0.9% produce isotonic condition for non-marine M.O
Hypertonic condition (high salt conc.) cause plasmolysis of cells
Both Mo and plant/meat tissues undergo plasmolysis result: shrinkage
Drying of meat and inhibit the growth or death of MO
Most non-marine MOs can be inhibited by 20% or less of NaCl
Salt effects are:
1. Causes high osmotic pressure and hence plasmolysis of cells
2. Dehydrates of foods
3. Ionize to yield the Cl-
which is harmful to MO
4. reduces the solubility of O2 in the moisture
5. Sensitizes the cell against CO2
6. Interferes with the action of proteolytic enzymes
CH3 CH3
CH3 CH3
Dr.rer.agr. BDR Prasantha, Dept. Food Science &Technology, Faculty of Agriculture, University of Peradeniya | 8
Sugars
Sugars also act as salt
But main differences is in relative concentration
One unit NaCl = 6 units of Sucrose
Sugars uses as preserving agents
e.g: Fruit preserves, Candies, Condensed milk
Yeast and molds less susceptible to sugars than bacteria
Yeast and molds can grow in the presence of 60% sucrose: Osmophiles or Osmoduric
INDIRECT ANTIMICROBIALS
Antioxidants
A molecule that inhibits the oxidation of other molecules
Oxidation can produce free radicals =>chain reactions => damage cells
Antioxidants : i.e: Thiols or ascorbic acid terminate chain reactions
Primarily to prevent the auto-oxidation of lipids
Antioxidants
Phenols (hydroquinone, pyrogallol, etc.)
Natural occurring substances
glutathione, ascorbic acid, vitamin E, etc.
shows antimicrobial activity for wide range of MOs
I.e. Bacteria, fungus, viruses, mycoplasmas and protozoa
High concentrations are required to inhibit MO in high-fat food
Some antioxidants increases the storage life of fats